Nuclear Production of Hydrogen, Fourth Information Exchange ...

NUCLEAR HYDROGEN USING HIGH TEMPERATURE ELECTROLYSIS AND LIGHT WATER REACTORS FOR PEAK ELECTRICITY PRODUCTION
Large differences in the cost of electricity versus time occur across the country, and significant
quantities of electricity are sold at high wholesale prices in grids such as ISO-New England, Florida
Power and Light, and the PJM grids. The greater the price differential between times of high and low
electrical demand, the more competitive a nuclear-hydrogen peaking system based on stored hydrogen.
If hydrogen is used for peak power production, the price of electricity at peak times must be
somewhere between 2 and 3 times that of input electricity for break-even economics to occur because
the round-trip efficiency of electricity to hydrogen and back to electricity is ~50%. Different markets
have different characteristics. Electric prices for the Los Angeles Department of Water and Power
show low-priced electricity [$10-15 MW(e)-h] for almost 1 500 h per year but high-priced electricity
(over 3 times higher) for over 5 000 h a year. This double-hump price curve reflects the low night-time
demand and the high daytime demand for electricity in Los Angeles. Were a nuclear-hydrogen peak
power cycle used in this system, the required hydrogen storage volume would be that needed to cover
one week of day–night shifts and weekday-weekend shifts in electric demand.
The electric prices for Seattle Power and Light show a similar double-hump curve, but the situation
is much different. The utilities in the Pacific Northwest have large quantities of hydroelectric power
that make it inexpensive to meet the variable daily demand for electricity. However, the utilities have
excess electricity in the spring, when the choice is whether to dump water over the dams or send it
through the generators to produce electricity. In contrast, in late fall hydroelectric power production is
low because the snow pack has melted and water flows have decreased. Fossil units with high
operating costs are used to meet the power demand at this time of year. If a nuclear-hydrogen peak
power system were used, the hydrogen storage volumes would be seasonal, reflecting the seasonal
characteristics of power costs in the Northwest.
Challenges and conclusions
In a carbon-dioxide constrained world there are many options to produce electricity (solar, wind,
nuclear, fossil fuels with carbon dioxide sequestration). However, all of the major options: i) have high
capital costs and low operating cost that necessitate operating at full capacity for economic electricity
production; ii) do not produce electricity that matches variable real-world electrical loads. Methods to
produce variable electrical loads to match electricity from capital-intensive technologies are required.
One set of options is using nuclear reactors to produce hydrogen at times of low electricity
demand, storing that hydrogen, and using that hydrogen for peak power production. If such a peak
power system were to be built today, the reactor would be an LWR, traditional electrolysis would be
used for hydrogen production, and a hydrogen version of the combined cycle natural gas plant would
be used to convert hydrogen to electricity. The round-trip efficiency of electricity to hydrogen to
electricity would be between 40 and 50%. With near-term improvements in electrolysers and the use
of oxy-hydrogen steam cycles, the round-trip efficiency would increase to between 50 and 60%. HTE
has the potential to further increase round-trip cycle efficiency by using heat to partly substitute for
electricity in the electrolysis process. Round trip efficiencies may exceed 60%. Simultaneously, a HTE
system can in principle be operated as a fuel cell for conversion of hydrogen to electricity. This capability
dramatically reduces capital costs – a high priority because peak power systems operate for a limited
number of hours per year.
There are significant challenges. In particular, the successful commercialisation of the high
temperature electrolysis fuel-cell technology is required. There are a set of auxiliary technologies that
can improve performance and economics if successfully developed. These include bulk oxygen
storage technologies and various oxygen-hydrogen to electricity technologies. Most of the other key
technologies are available. The development of peak-power electric technologies would significantly
enhance the competitiveness of all high-capital, low-operating cost electric generation technologies:
base-load nuclear, fossil fuels with carbon sequestration, wind and solar.
NUCLEAR PRODUCTION OF HYDROGEN – © OECD/NEA 2010 163